The long range objectives of this research are: (1) to achieve understanding of optical phenomena in complex molecular systems, including electronic absorption and circular dichroic spectra and related effects arising from polarizabilities of molecules and the surrounding medium; and (2) to develop an improved basis for interpreting such phenomena in terms of molecular structures. The specific aims are: (1) to extend the normal mode method developed in this project to the treatment of more general multipole interaction models; (2) to apply the multipole interaction theory to the calculation of absorption and circular dichroic spectra of molecules containing aromatic and other unsaturated chromophores, with particular attention to distributed monopole interactions; (3) to use parameters obtained for purine and pyrimidine chromophores to predict absorption and circular dichroic spectra of nucleic acids in various conformations; (4) to apply the cavity theory of solvent effects on spectra developed in this project to tbe calculation of spectra of helical polypeptides, linear conjugated molecules, and other molecules for which spectra are known to be affected by solvent; and (5) extend the theory to related phenomena, including magnetic effects and interactions of chromophores whose electronic spectra have arbitrary band shapes. The importance of this project to the health sciences lies in its bearing on phenomena that are widely used to study structure and interactions of complex biomolecules.